There are few things in life you have control over, but THIS IS ONE OF THEM.
You are the only one who can guide the introductions to ensure that your new dog and your dog or dogs in your home have the absolute best chance of co-existing peacefully and happily. To throw dogs together and “let them work it out”, is an urban myth. DON’T DO IT. Dogs who are new to each other are often anxious, over-excited and stressed and that state of the mind is the perfect setup for dogs on both sides to make bad choices.
By taking the time and effort to remove that excitement, stress, and anxiety from the interaction -- while giving them human guidance -- sets them up for success, not failure. These are guidelines; they are flexible according to how well adjusted your present dog or dogs are, and the temperament of your new dog.
FIRST, KEEP THEM SEPARATE. Your new dog should NOT be introduced to your present dog or dogs right away.
CRATE your new dog when not being walked or fed, or given playtime (with you, not your dogs). All the dogs will be aware of the other’s presence through sight and smell. You can eventually use a baby gate to let them sit alongside each other. If they do so peaceably, in a sit, they’re rewarded with treats.
Feed separately, or in crates. All bowls picked up after eating. AND no toys, no bones, no chewies left around. Until you are absolutely confident your dogs will not resource guard with each other, it is just not worth the risk. (And it might never happen, so it might be a permanent practice. )
After a few days, if all is going well, get them out together. Get someone to help you, at least for the first few times. Each takes a dog. Leash up, dogs on the outside, humans in the middle. Walking as a pack is the most therapeutic act there is for a pack of dogs. It is a bonding experience on all fronts, your dogs, and your dogs and you. After a few successful walks, you can try sniff intros. Again, have someone help you. Use your most calm, balanced dog first if you have more than one. Let them sniff butts. Always do it away from home, on neutral territory.
Only when and if the dogs have exhibited calm, respectful behavior with one another. This step might take weeks (even months) after your new dog arrives. Be aware of canine body language. Some common signs of stress: stiff body, high, stiff tail, closed mouth, lip licking, growling, lip lifting. If you notice any humping, escalation of play, dominance standing, separate calmly and save it for another day.
TAKING IT SLOW SETS THEM UP FOR SUCCESS, NOT FAILURE.
The slower you take it, the greater chance of successful integration. You might think (or want) your dogs to get along right off the bat, but chances are if you put them together too quickly, that relationship will get off on the wrong foot. You want this to work out and work out well. For that to happen, YOU have to be the one who exercises control, patience, and sense. Your dogs depend on you, and you need to step up!
We have borrowed extensively and freely from the N.I.L.I.F. program from Bad Rap in San Francisco (Nothing In Life Is Free) and from trainers such as Sean O’Shea, Julio Rivera, and Tracy Baldwin.